A typical photovoltaic generation system is configured with a solar cell array in which a plurality of solar cell modules are connected, a junction box, a power conditioner, or the like.
PID (Potential Induced Degradation) which will be described later and which becomes a problem in recent years in the above-described photovoltaic generation system mainly occurs at a crystalline solar cell module.
A crystalline solar cell module is made by sealing solar cells each having single-crystal or polycrystalline silicon substrate interconnected with a tab wire, with a seal material such as EVA (Ethylene Vinyl Acetate), further, sandwiching the sealed solar cell between a white tempered plate glass and a back sheet and laminating the sandwiched solar cell. Because a solar cell module normally requires a certain degree of intensity, an aluminum frame is attached around the solar cell module.
As a typical crystalline silicon solar cell, for example, there are crystalline silicon solar cells as disclosed in Patent Documents 1 and 2. Particularly, in the crystalline silicon solar cell disclosed in Patent Document 2, a p-type single-crystal or p-type polycrystalline silicon substrate is used, a light receiving surface electrode and a non-light receiving surface (back surface) electrode are respectively formed with silver paste and aluminum paste as materials using a screen printing method, a silicon nitride film which is an antireflective film on the light receiving surface is formed using a PECVD method, and, further, a diffusion layer which forms pn junction on the light receiving surface side is formed by thermal diffusion using POCl3 gas (phosphorous source gas).
In this photovoltaic generation system, solar cell modules are connected in series such that a voltage of the solar cell array can increase to a necessary voltage. Further, in order to prevent an electrical shock and a fire accident due to electric leakage from solar cell modules, earth wires are extracted from metal frames which enclose the solar cell modules and connected, and one end of the connected earth wire is connected to a grounding electrode.